Japanese Patent Application Publication No. 09-218055 (JP09-218055A) discloses an absolute encoder including a combination of a resolver and a magnetic encoder device including a gear mechanism. A circuit substrate having a signal processing circuit mounted thereon and the gear mechanism of the magnetic encoder device are disposed in the same housing portion of a housing.
Japanese Patent Application Publication No. 08-050033 (JP08-050033A) discloses an absolute encoder including an optical encoder device formed by utilizing a single rotary disc and a magnetic encoder device.
In such absolute encoders as disclosed in JP09-218055A and JP08-050033A, multiple rotations are detected by a position detecting device formed by the magnetic encoder device.
In order to store data on the multiple rotations without using a battery in an absolute encoder including an optical encoder device and a magnetic encoder device as is disclosed in JP08-050033A, it may be necessary to adopt a gear mechanism in the position detecting device as is disclosed in JP09-218055A. However, if the gear mechanism and other constituent parts are housed in the same housing chamber of a housing as is disclosed in JP09-218055A, the rotary disc or other parts used by the optical encoder device may be contaminated with abrasion powder produced by friction between gears or grease applied to reduce wear of the gears, which may trigger erroneous detection.